Transportation of respiratory gases

v. Hb4O6 75%

vi. Hb4O8 100%

ie. The Hb molecule can combine with a different numbers of O2 molecules.

Oxygen dissociation curve for Hb.

Saturation

Of Hb

(%)

p.O2 ( mm.Hg)

p.O2 =partial pressure of oxygen . mm.Hg = scale Hg= mercury

The graph describes the behaviour of the haemoglobin molecule in the way it binds with oxygen in different environment.

- Haemoglobin in red blood cells is exposed too a high pp of oxygen ( around 100mm of mercury).The graph shows that Hb molecules here will be fully saturated.

2- Red blood cells containing saturated Hb now travel in circulation until eventually exposed to a lower pp of O2 where cell actively respires.

3- Hb is obliged to release the oxygen it carries that represents the difference between point 3 and 100% saturation ( point 4)

4- Represents the amount of O2 given up by the Hb molecule that is now free too diffuse into the respiring tissues.

Hb is a complex molecule that has evolved to O2 and only deliver it to cells where it is required low p.O2.

Bohr effect/ Shift

Hb delivers oxygen to the respiring tissues as described but in the body the delivery is fully enhanced by the Bohr shift.

Saturation

Of Hb

(%)

p.O2 (mm.Hg)

- As before because haemoglobin is not exposed to less alkali conditions.

2- Hb and red blood cells arrived in respiring cells where Ph is lower.

3- This requires us to use the red curve.

4- Wee can see that more oxygen will be dissociated than would have been if the PH had not been lower.

Thus the Bohr shift is an enhancement of the oxygen dissociation curve that delivers more O2 to those tissues that require it the most.

i.e. the Ph begin lowered makes Hb dissociate more O2.